The present invention relates to a magnetic head for magnetically recording and/or reproducing a video signal, and a method for manufacturing the same. More particularly, the present invention relates to a magnetic head of a structure adapted for a high density recording and a method for manufacturing the same.
In an apparatus for magnetically recording and/or reproducing the video signal such as a video tape recorder (VTR), a high density recording is required to efficiently use a magnetic recording medium or a magnetic tape. For this purpose a very small head chip having a gap width (i.e. length of gap measured longitudinally of a record track) of less than 1 .mu.m and a track width of less than 100 .mu.m has been required. Moreover, these dimensions must be machined with a high precision. In this case, if the thickness of the head chip is reduced entirely to an extent comparative to the track width, a cross sectional area of the core is so reduced that the reluctance of the core increases resulting in the decrease of a reproducing efficiency of the head. In the past, for this reason, the head chip having such small gap width and track width has been designed to have a structure as shown in FIG. 1. Namely, the thickness of the head chip, that is, the thickness Tc of the core has been selected to be three to four times as large as the track width Tw to reduce the reluctance of the core. (The drawing schematically shows the shape but the relation of the respective dimensions is not exactly indicated.)
A method for manufacturing the head chip of FIG. 1 is now explained with reference to FIG. 2. A pair of elongated rectangular bodies 1a and 1b of magnetic material having approximately 2 mm by 8 mm in size and approximately 1 mm in size are prepared. The magnetic bodies may be made of Mn-Zn single crystal ferrite or high density ferrite. One major surface of each of the elongated rectangular magnetic bodies is polished to a surface smoothness in the order of 0.05 .mu.m or less. As shown in FIG. 2a, a polished surface 2b of one magnetic body 1b is formed with a channel 3 which serves as a window in winding a coil. Then, SiO.sub.2 or Al.sub.2 O.sub.3 layers as gap defining layers are formed to the thickness of 0.4 .mu.m, for example, on the polished surfaces 2a and 2b which are to subsequently form a head gap. This may be formed by an R.F. sputtering method or the like. The magnetic bodies 1a and 1b are abutted to each other with the gap defining layers facing to each other and bonded by fusing glass therebetween to form a bonded block 4 having a gap width of 0.8 .mu.m as shown in FIG. 2b.
Then, as shown in FIG. 2c, chips 5 each having a thickness of 250 .mu.m, for example, are sliced from the bonded block 4. Finally, as shown in FIG. 2d, an arcuate groove 6 is formed such that a predetermined track width Tw (e.g. 60 .+-. 5 .mu.m) is established near the gap g. The length Td of the arcuate groove should be larger than the depth of the gap.
The arcuate groove 6 may be ground by a high speed grinding of in the order of 3,000 r.p.m. using a rod having a diameter of 1 mm, for example, on which diamond particles are attached. The grinding process may be observed through a microscope.
In the manufacturing method described above, if the center of the grinding rod is not exactly positioned at the gap, the track width changes even if the grinding depth is kept constant. Accordingly, the precision of the machining of the track width is low and a yield is less than 50% for the track width of 60 .+-. 5 .mu.m, for example. Furthermore, because of the occurrence of crack or chipping at portions of the magnetic bodies during the machining process, the overall yield is further lowered. Moreover, since the machining process for establishing the track width Tw must be carried out for each of the head chips 5, long manufacturing time is necessary, which eliminates a low cost head.